Studies of pre- and postimmunization antibodies of sheep

Serum samples were taken serially from three nonimmunized sheep over a long period of time. Antibodies to human serum albumin (HSA), ovalbumin (OA) and FITC were separated from the samples. Than, two of the animals were injected with HSA+ complete Freund's adjuvant, the third with adjuvant without antigen. Serial postimmunization serum samples were subjected to the same procedures as the pre-immunization ones. The specific antibodies increased in concentration, and only the postimmunization antibody population was able to precipitate. In the presence of the antigen, the postimmunization antibodies bound to the Fc receptors of lymphocytes to an increased degree. There was no difference between pre- and postimmunizaton antibody populations either in complement-activating capacity or in the quantity of antigen necessary for reaching antigen-antibody equivalence. Isoelectro-focusing showed no new bands which would indicate antibodies different from the pre-existing ones. However, changes were observed in the relative participation of the antibodies forming different bands. No sharp limit was observed between pre- and postimmunization antibody populations. The Ig increment demonstrated after immunization was accompanied by a similar increment in the specific antibodies tested in the animal that had not given antigen, but not in the others. The authors attribute a role to humoral antibodies already in the earliest phase of immune response.